The present invention relates to methods and compositions useful in emulsifying and feeding sizing agents into a process stream of a papermaking process. Compositions such as alkenyl succinic anhydride (ASA) and alkyl ketene dimer (AKD) are papermaking additives, which enhance a number of hydrophobic paper properties in paper products. The application of these compositions in a papermaking process to introduce these hydrophobic paper properties is called sizing.
Sizing is important both in the papermaking process as well as in the final use of the produced paper product. For example, the extent to which a paper is weakened by the rewetting stage at a size press device during papermaking is influenced by its sizing. Also the structural integrity of a paper product that comes into contact with water is affected by its sizing. As a result food and beverage packaging typically undergoes a high degree of sizing because of the regular contact that occurs between the packaging paper and water.
Generally a sizing agent is introduced during the wet end of a papermaking process. Sizing agents such as ASA are insoluble oily compositions. As a result, they must be emulsified prior to introduction to a papermaking process. Currently a number of technologies are used to facilitate the emulsification of sizing agents in papermaking processes.
In order to adequately emulsify a sizing agent for a papermaking process, two requirements must be met. First, the resulting emulsion must impart on the produced paper good sizing properties. Second, the emulsion must also be easily applied to papermaking machines. Prior art methods of forming emulsions include: mechanical processes such as those described in U.S. Pat. No. 7,938,934 and European Patent EP 0961856 and chemical processes such as those described in U.S. Pat. Nos. 4,657,946 and 4,529,447.
One deficiency in some chemical emulsification processes is what can be called the “overdose effect”. Prior art in chemical emulsification processes often possess a maximum dosage. When the dosage of the chemicals is increased up to the maximum dosage their effectiveness (as measured for example according to the HST or Hercules Sizing Test) also increases. However once the maximum dosage has been reached the further additions of these chemicals has negligible or no improvement. This overdose effect limits the overall effectiveness of sizing agents in papermaking processes.
Thus it is clear that there is a clear utility in novel methods and compositions for the emulsification of ASA for sizing applications. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.